This invention relates to exhaust systems and, in particular, to mufflers for controlling and reducing noise associated with engine exhaust gas. More particularly, this invention relates to stamp-formed mufflers having internal stamped sheet metal tuning plates or a plurality of tuning tubes fixed inside a muffler chamber formed by two mating external shells and rigidifying mechanisms for the external shells.
For several years, mufflers have been constructed using stamp-formed sheet metal shells and plates. Although some conventional stamped mufflers can be assembled using fewer component parts than conventional tube mufflers, it is nevertheless recognized that it is necessary to modify the design of conventional stamped mufflers to improve the manufacturability and noise management qualities of stamped mufflers. For example, it has been observed that weld process time for assembling conventional stamped mufflers is high and that it is often necessary to to rely on costly, space-consuming, and labor-intensive welding equipment to assemble conventional stamped muffler components. It will be appreciated that the unit cost of each stamped muffler can rise significantly if the weld process time allocated for muffler assembly is very large.
All mufflers vibrate during use because of irregular pulsation of high-temperature, vehicle exhaust gas conveyed through the muffler chambers and passageways. Such pulsations are known to vary between 25 and 300 cycles per second in an irregular pattern and create muffler shell vibration and noise. Stamped mufflers are particularly susceptible to excessive shell noise problems due, in part, to a lack of adequate internal support structure for the muffler shells.
Shell noise is often produced because one or both of the outer shells that are joined together to form the outer skin of the muffler flex during movement of hot exhaust gases through the muffler. Numerous factors such as basic shell design, material gage, and unsupported spans between baffles provided in a muffler contribute to creation of shell noise during muffler operation. Further, in some instances, where no or few internal baffles are installed or present in a muffler, the frequency of shell noise problems can be significant.
According to the present invention, a muffler assembly includes a pair of half shells, at least one plate disposed in an interior region between the shells, and at least one rigidifying structure extending between the at least one plate and one of the shells to support the shell without dividing the space between the plate and the shell into a further subchamber to rigidify the muffler assembly and reduce flexing of the shell relative to the plate. Advantageously, provision of such a rigidifying structure can lead to a reduction in shell noise without creating any more subchambers in the interior region of the muffler assembly.
In one embodiment of the present invention, a muffler assembly includes a first shell half and a second shell half attached to the first shell half at a perimetrically extending split line to define an enclosed area therebetween. The first and second shell halves cooperate to define a flange-receiving space therebetween at the split line. An inlet port is provided in the muffler assembly for admitting exhaust gas into the enclosed area and an outlet port is also provided for expelling exhaust gas from the enclosed area.
A first inner tuning plate is disposed in the enclosed area. The first inner tuning plate has a flange edge trapped in the flange-receiving space to retain the first inner tuning plate in a fixed position dividing the enclosed area into a first chamber between the first inner tuning plate and the first shell half and a second chamber between the first inner tuning plate and the second shell half. A second inner tuning plate is also disposed in the second chamber.
The first and second inner tuning plates each have channel-forming depressions which cooperate to define exhaust gas conducting tubes connected to the muffler chamber inlet and outlet when the plates are joined together. Means is provided for attaching the second inner tuning plate to the first inner tuning plate in piggyback relation to provide the exhaust gas conducting tubes. The second inner tuning plate is thereby retained in mating engagement with the first inner tuning plate without extending into the flange-receiving space at the split line so that only the first shell half, second shell half, and first inner tuning plate are rigidly joined together at the split line. Once joined together, the channel-forming depressions in the first and second inner tuning plates are aligned to form tubes for conducting exhaust gases therethrough.
Advantageously, the inventive muffler assembly is made of stamp-formed components which can be assembled quickly and easily without using costly complex welding techniques. The muffler assembly is also constructed to reduce shell noise associated with vibration occurring during muffler use.
The invention contemplates, for example, providing a rigidifying structure connecting at least one of the depressions on one of the inner plates to its adjacent half shell to rigidify the half shell. This feature will help to eliminate shell noise caused by flexing of the shell during passage of engine exhaust product through the muffler. Shell flexing is of course determined by the basic shell design (e.g., support rib locations if any, material and thickness of material, distance between supports, speed and pressure of exhaust gas flow, resonant frequency of engine and muffler, etc.).
It is also contemplated that each channel-forming depression could have a rigidifying structure or only those channel-forming depressions adjacent long unsupported spans of the half shells would be provided with rigidifying structures. Preferably, the rigidifying structures extend from the channel-forming depressions since their outer surface is closest to the unsupported half shell and this would reduce the size, weight, and material necessary to create the rigidifying structure. Alternatively, it is possible to connect the rigidifying structures to the tuning plates between adjacent depressions. Also, the rigidifying structures can be fitted with holes to allow for welding.
It is contemplated that the rigidifying structure could be raised portions drawn or pressed from the material that makes up the depressions and/or the half shells. Alternatively, an extra piece of material could be inserted between the half shell and the depression to form a rigidifying structure.
It is important to minimize the effect on chamber (sub-chamber) volume by these rigidifying structures and accordingly they are made to extend over a small cross-sectional area of the chamber (sub-chamber) so as not to reduce its volume and hence maintain nose abatement and acoustic control.
In other embodiments, the muffler assembly includes a plurality of flow tubes and baffles placed in the interior region between the shells to control the flow of vehicle exhaust gas through the muffler assembly. Such a hybrid tube and baffle design is also susceptible to shell noise problems, and provision of one or more rigidifying structures in accordance with the present invention can lead to a reduction in shell noise.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.